This invention relates to a call connection control method in an exchange. More particularly, the invention relates to an exchange for performing call connection control for subscribers in a plurality of areas having different toll numbers, as well as to a method of performing call connection control in this exchange.
The number of telephone subscribers accommodated by a single toll number in a sparsely populated area is very small in comparison with that of a city. Accordingly, since deploying an exchange for every toll number would raise cost, it has been sought to control a plurality of toll numbers by a single exchange through use of a remote line concentrator or the like. However, the following problems arise when a plurality of toll numbers are controlled by a single exchange:
1) If an exchange having a control function for only one toll number is provided with a function for controlling a plurality of toll numbers, this will require large-scale expansion of data memory and modification of software. PA1 2) In regard to a service call (to a police station or fire station, etc.) based upon a special service number, the prior art is such that regardless of the toll number area from which the call originates, the call is terminated at a centralized special service number reception center and cannot be terminated at a special service number reception center located in the same area as that of the subscriber that originated the call. Depending upon the customer, however, there is sometimes a desire to terminate the call at a special service number reception center located in the same area as that of the originating subscriber. PA1 3) In a case where different services are provided, the conventional practice is to provide a number for supporting each service. Depending upon the customer, however there is sometimes a desire to receive different services on the basis of subscriber attribute using the same service number. Such requirement cannot be met with the conventional schemes.
Problems 1) through 3) mentioned above will now be described in greater detail.
1) Need for Large-Sale Data Memory and Software Modification
FIG. 18 is a diagram showing the configuration of a telephone network in which toll number areas each have an exchange. A toll number area (045 area) TCA1 has a toll number 045, and a toll number area (044 area) TCA2 has a toll number 044. The 045 area TCA1 includes local areas LA11, LA12 and LA13 having 111, 112 and 113 as local office numbers, respectively, and the 044 area TCA2 includes local areas LA21, LA22 and LA23 having 221, 222 and 223 as local office numbers, respectively. An exchange TEX1 is provided in the 045 area TCA1 and has a telephone number translation table NTT1, and an exchange TEX2 is provided in the 044 area TCA2 and has a telephone number translation table NTT2. A centralized special service number reception center SNR accepts a special service number such as 110 (police station) or 119 (fire station). A special service number reception center SNR1 is provided in the 045 area, and a special service number reception center SNR2 is provided in the 044 area.
If the two toll areas TCA1, TCA2 shown in FIG. 18 were to be controlled by a single exchange, it would be necessary to provide the exchange with the telephone number translation tables NTT1, NTT2. Assume that there are 64 local office numbers in each of the toll number areas and that 10,000 subscribers can be accommodated by each local office. This means that a telephone number translation table is required to have 64.times.10,000 storage areas per toll number area. Combining two toll number areas would require 2.times.64.times.10,000 storage areas. Thus, the memory that stores the telephone number translation table would need have a very large storage capacity.
FIG. 19 is a diagram useful in describing the structure of a telephone number translation table in a case where ten toll number areas are combined. Here a table NTTa accommodating toll numbers, a table NTTb accommodating local office numbers corresponding to one toll number and a table NTTC accommodating subscribers corresponding to one local office number are required to have ten storage areas of 0.about.9, 64 storage areas of 0.about.63 and 10,000 storage areas of 0.about.9999, for a total of 10.times.64.times.10,000 storage areas. Thus, in a case where an exchange having a function for controlling only one toll number is provided with a function for controlling a plurality of toll numbers, a large-scale data memory is required.
Further, in a case where the two toll number areas TCA1, TCA2 are controlled by a single exchange EX, as illustrated in FIG. 20, it is necessary to perform call connection control in such a manner that (1) if the calling party and the terminating destination reside in the same toll number area, the call can be placed without transmitting the toll number; (2) if the calling party and the terminating destination reside in different toll number areas, the call cannot be placed unless the toll number is transmitted. For example, in order for a subscriber A to place a call to a terminating destination B residing in the same toll number area (the 045 area) TCA1 as that of subscriber A, subscriber A need only dial the telephone number 112-1001 of subscriber B. In order for subscriber A to place a call to a terminating destination C residing in a toll number area (the 044 area) TCA2 different from that of subscriber A, subscriber A must dial the telephone number 044-221-1001, namely the number onto which the toll number has been added. The reason for performing control in this manner is as follows: If the calling party A calls the number 112-1001 in a case where a subscriber D having the telephone number 112-1001 is present in the 044 area TCA2, the exchange EX may not connect the path between A and B and may instead connect the path between A and D by erroneously. In order to perform such control, a large-scale software modification is required.
2) Necessity to Terminate Call at Special Service Number Reception Center in Same Area
In the telephone network shown in FIG. 18, a call is terminated at the centralized special service number reception center SNR regardless of whether the special service number is transmittedfrom toll number area 045 or 044; an originating subscriber cannot be terminated directly at the special service number reception center SNR1 or SNR2 in the same area. More specifically, when subscriber A in toll number area TCA1 of the arrangement shown in FIG. 21 dials a special service number, first the call is terminated at the centralized special service number reception center SNR, after which the call can be placed by establishing a path between subscriber A and the special service number reception center SNR1 in toll number area TCA1 as necessary. With this special service number connecting scheme, however, a subscriber in the 045 area TCA1 will no longer be able to transmit a special service number if it becomes impossible for the exchange TEX1 to communicate with the centralized special service number reception center SNR due an earthquake or for some other reason. Similarly, a subscriber in the 044 area TCA2 will no longer be able to transmit a special service number if it becomes impossible for the exchange TEX2 to communicate with the centralized special service number reception center SNR due an earthquake or for some other reason.
3) Conversion of service number
There is demand for provision of different services, through use of the same service number, based upon the attribute of a subscriber without modifying the service number plan. For example, a three-digit international telephone service number "001" is prefixed to the destination telephone number xxxxxxxxx when an international telephone call is made. When the international telephone call is placed using this number, the registered bank account of the subscriber is billed the fee at regular intervals. However, if a three-digit number "002" is prefixed to the destination number and a credit card number is added onto the end of the destination number when the international telephone call is made, a bank account in accordance with the credit card number will be billed for the call. This is a service now available and is convenient when one is on a journey and uses another person's telephone to make an overseas call. However, there are certain subscribers who wish to use the number "001" for the latter service as well. More specifically, for a certain subscriber the special service number 001 is for a domestic telephone service through which an account conforming to this subscriber's credit card number is billed for a telephone call. For a different subscriber, however, the service number 001 is for an international telephone service in which the account billed is that for which a contract has been made with the telephone company.
Thus, in a case where similar services are available, there is a need to provide different services, even though the service numbers are identical, on the basis of subscriber attributes.
Thus, in a case where a plurality of toll number areas are controlled by a single exchange, the prior art is such that a large-scale data memory is required as well as large-scale modification of software.
Further, if it becomes impossible for an originating subscriber and a centralized special service number reception center to communicate, a problem which arises in the prior art is that a call from this originating subscriber cannot be terminated at the special service number reception center located in the same area.
Further, though there are cases where certain subscribers wish to receive different services even though the service number used is the same, the prior art is incapable of satisfying this need.